1. Field of the Invention
This invention relates to a cable for fastening structures, more particularly a cable for mooring offshore floating structures, suspending bridges and supporting buildings, and to a method of detecting damage to the corrosion-preventive layer thereof.
2. Description of the Prior Art
For, example, the mooring means for fastening offshore floating structures employed in the exploration of submarine oil fields etc. are required to have high enough durability to remain in service for as long a period as 20-30 years. Accordingly, steel chains are used extensively in this application.
On the other hand, parallel-wire cables used with suspension bridges and other ground structures are counted among the most excellent tensile structural members on account of their high breaking and fatigue strength and large modulus of elasticity. The parallel-wire cables may be used for mooring offshore structures, but then they must be covered with polyethylene or other suitable material to keep them out of contact with seawater so that their excellent properties mentioned before may be maintained over a long period of time. Namely, preliminary provision of a protective or corrosion-preventing coating or film is indispensable.
When such preliminarily coated parallel-wire cables are used for mooring, it is necessary to check from time to time to determine if their properties remain unchanged. The key point of the check is the presence of damage to the corrosion-preventive layer. If the corrosion-preventive layer is damaged, seawater might penetrate inside and contact the cable, with the result that the cable might get corroded and broken after a while.
The same can be said of the wire ropes consisting of a plurality of strands and covered with a corrosion-preventive layer.